Rectifier tube



@1%. Percy LgzspencenrNewton, Mass.,.assgnor,' by f mesne` assignments, `to Raytheon Manufactur-- -ingompapm Newton, Mas-aarporation; f

f Y` 4"`Application Jury' s, 1927; seal No; 204,320

f RenewedlMayjQ, 1930 l14,lolaime (oilesdozas) AMy invention relates generally to gaseous'conduction apparatus and in particular tozf the type of "device thatV employs a1 'mixture'off gases" to facilitateV starting and improve operation." l

af less? nionizable gas, theV4 former y takesV "onf the function ofgettering or cleanfu'pfin addition'to producing g the lowcathode drop necessary for starting andrefcient-operation. Asa result the vaporizable substancebecomes inactive 'ina r'elatively short time unless k'considerable Aquantity ofthe material is present. Inasmuchas the 'sub stances found most suitableV forinitiating `disr` charge, e. g. caesium and rubidium, are costly and difcult toobtain, `it is advantageous to relieve these; metals of the igetteringfunction;assign? ing Vthe latter, wholly or partgton acommon element which will in no Ymanner detractrom the advantages oiered by the more active` `mate- Now;n I Ahave 'discovered that itis practical to employ a relatively small amount of an expensive highly active Valkali 4rnetal 1 and preventits de# activation by residualgases. In brief,1 this is acconlplished by mixing withu the cae'siuni or other Veasily ionizable material', al less electropositive yand costly alkali, e,`g.jpotassium;which readily assumes the work of clean-up without Y interfering with theelectron liberating fproperties offthecaesium. Q v V1 ,.7 "Thefprimarylobject of my inventio'nis' to re# duce theA cost of gaseous conduction apparatus;

' 'Another object `isto employlminimurvnfamount of `highly active, expensive"allgaliy metals for' producing discharge;A Av further object is to provide in addition to,r thej usualinert'gas fill,- ing,` amediumoftwo or morealkali vapors,` one ofwhich serves exclusivelyfto ,facilitatejstarting and another of lower cost ltorexnove residual gases.,A A still further object isf-tofpr'ovide an eflicient and convenient'method of introducing ancfvaporizing the alkali metal mixture; other objects and features will be apparent as the fol;V

` lowingcontextis perused in connection with the accompanying drawing Vwhich illustratesY apreferred embodiment. Y

The type'of discharge apparatusexemplied in the drawing is a full wave rectier and employs an envelop l which may be formed `of glass, hollow cathode 2 of tantalumor other refractorymaterial, anodes 3 also of refractory material, insulating thimbles 4 preferably of Y lavite, and a base comprising metallic cylinder V'additional alkali metal, of which potassium isvbut 5- secured by suitable compound to the *envelop in 'the Vusual manner.V 'Ihe Ybottom ci 'thejcyl inder is closed by insulating disk 6 intofwhiclrv y thefconnectorvplugsproject. lThe envelop? I fleas 5 `It has been-found that whenithe source vof` space current `carriers @derived-from an easily. ionizable vapor such as alkali metal vaporV and bers concentrically with projections il and operi- 10:l

Vings 9 in the'cathode, the spacing betweenganodes y and cathode being preferably ofrtherorderf dior less than the mean free path of electrons in fthe space.- The cathode is preferably Vformed ntwo parts, the upper part taking on :1r/partially closed shape; as conical or elliptical and the' lower part l! a cover fitting the open end vof the 'other part'. I A portion of each thimble "4' is spaced'fromth anodes adistance'of the order ofl or lessthra'n the meanfree path ofthe electronsrpresent and serves to prevent the Ypassagefof current between either anode andthe outer surface of jthe cathode.- fThe gas employedfmay be'anyfonel or aVY` combination 'oftwo or more of the inmatornie group, although I preferheliuijnat ,theA pres- 2`5^ sure of Y,severalmillimeters or mercury.u Y l In order to reducethe voltage lossl'proposeto 'irnmersethe electrodes in ahighly active alkali metal vapor such as caesium and to restrain the latter from assuming theV role of getter. 'The amants preferably' 'introduced by the4 `cgflpsme method, the vapor being `liberated-in a manner- 'stated hereinaften With thecaesium in, capsule [31a quantity of another andrlessexpensive::alkali metal substance is provided, e. g.l potassium;hav; ing the specic function'of removing the `residual gases, vleaving to the caesium substantiallythe sole function of activating the-cathode.

an example, *isV as is well known less electropositive and of a lower atomicrweight than' caesium, and also has a greater afnity for impurities` than has caseium.

, A convenient methodI of combIiiIfll;` the "alkali fis vbymixing"caesium chloride and potassium chloride and melting them `together' in anickel crucible.Y After theV fused mass is powderedup, itis placed in Vthe capsule together with calcium rchipsror other reducing material in suitable form,

e. g. as pill lll.V I have found that one part caesium chloride to twenty parts potassiumchloride functions well through I prefer to use one I to ten ratio;V The capsule I3, which is formedrof two hemispherical portions secured together in a.

manner to allow gas leakage, is positioned within 5 ww V j v 1:1artment for heating thelatter. 2. A substance forinitiatingrdischarge .in aV the container by being welded to the end of a lead wire sealed in the stem and connected to a plug projecting through the base. By mounting capsule I3 in this manner, it is possible to connectV a sourceof potential to it and other electrodes within the envelope and thus initiate a discharge therebetween. f

After the tube is sealed from the pumping sys-v tem and helium or other inert gas admitted, an electrical discharge is passed between electrode 'I0 and the juxtaposed capsule. The bombardment causes the metal of capsule I3 to glow from whichY heat is thermally transferred to the enclosed pill, liberating the alkali metal vapors. The latter may enter the hollow cathode'through line apertures l5 in the cover. While the action Vof the mixture may not be clearly understood at present, the indications point to the fact that caesium and potassium do not alloy but act as individual elements in the tube, hence the vapor pressureof one is not greatly affected by that of vthe other. Moreovergwith the tube not operating and alkali metal condensed on the walls, the

oxygenousor other deleteriousgases appear to pass through the covering layer of .caesium and are immediately absorbed by the potassiunn In operation the caesium evidently adheres to the cathode surface, i. e. within the cathodal chamf v ber, end0wingthe rectier with properties similar to those produced by a relatively great and inexhajustible supply ofpure caesium. The potassium may or may not assist in lowering the voltage drop but it unquestionably takes on `the greater part, if not all, of the burden of cleaningup the gaseous impurities'.

- It will be evident that the invention is not limited specically to caesiumand potassium, but embraces all instances in which one alkali metal is used for.- the purposeY of activating a cathode surface and lowering its drop, and a second less electropositive alkali metal usually of lower atomic weight isused to prevent said rst-named alkali metal from losingitsactivating proper-f ties.' Thus various modiiicaticns ofthe speciiic modication described abovewill be evident to those skilled in the art. It is accordingly desired that the appended claims be given a broad inter'- pretation commensurate"withV the vscope of the invention 4'within the art.-

I claim: s l. A gaseous discharge device comprising .the

combination of a plurality of electrodes, Van inert gas,A a mixture of caesium and potassium chlorides Vanda reducing` agent in a metal compartment positioned in juxtaposition l to one of the electrodes and meansfor initiating annelectrical dis.- .chargebet'ween said one electrode and thecomgaseous discharge device'a'nd for removing residualgases comprising a fused mass containing caesilnnA chloride andpotassium chloride and a reducing agent. 3. In an/ electric discharge device comprising a hermetically sealed envelopeV containing la4 cathode,'an anode, the method of activating the surface of said cathode and cleaning up impurities in said device which comprisesheating a mixture Va reducing agent.

of a compound of caesium, a compound of aI1- other alkali metal having a greater anity for said impurities .than caesium, and a reducing agent to a temperature at which these alkali metals are liberated within said envelope.

4. A getter for electric discharge devicescomprising a mixturerof a compoundvof lcaesium, a compound of another less electro-positivev alkali metal, and a reducing agent. V

5. A getter for an electric discharge device comprising .a mixture containing'one part of a compound of caesium and vfrom ten to twenty parts of a compound of-potassium together with 6. The method of activating a metallic cathode for electronemission purposes and cleaning up v residual gases and kvapors in an electron discharge device of the caesiated cathode type, comprising heating to reaction temperatures in the device a mixture of a compound of caesium and a compound of potassium with a reducing vagent to liberatethes'e metals in thedevice. 4 l

V7. A getter for electronV discharge devicesemploying vcaesium therein, comprising a mixture or a compound of ca ,esiunfiV anda compound o f another alkali metal of lower atomic weight mixed with a reducing agent.

8. A getter for electron dischargedevicesemploying caesiumtherein, comprising a .mixture of a compound of caesium and acompound. of potassium mixed with'a'reducing agent. 9. Thesteps in the method ofl producing an electrical discharge device employing a caesiated cathode which 'comprises introducing into the device a mixture'of a reducible .compound o f caesium anda compound Vof another alkali metal of lower atomic weight with a. reducing agent and heating the mixture to liberate the alkali metals in the device. l

l0. The steps in the method of producing an electrical discharge device employing a caesiated cathode which comprises liberating in the device from chemical compounds of which theyare elements av quantity of caesium and another alkali Vmetal which forms more 'stable compounds with 12. 'A getterl forr electrical' discharge devices comprising a mixture of a compound of z an'alkali metal, a' compound of,y another'less electro-posifY Y.

tive alkali metaLanda reducingy agent.

13; A getter Y' for electron discharge devices comprising a mixture of Va compound ofan alkali metal, and a compound ofv another alkali metal of lower vatomic weightA mixed ywith*A an reducing agent.V ,l

14.YV The steps inthe method of producing an electrical discharge device which comprises introducing into the device a mixture of a reducible compound of an alkali metal and a compound of another alkali metal of lower atomic weight with a reducingv agent,v and heating the mixture liberate the alkali metals inthe device.

PERCY I J. SPENCER. 

